Method for making available features for alternative connections of primary connections

ABSTRACT

The invention relates to a method for creating alternative routes to primary connections, particularly to voice-over IP connections, in which the data transmission occurs in a primary network, and an alternative data transmission occurs in a, as a rule, less efficient secondary network. According to the invention, a system architecture with geographically distributed gateways can be used, said gateways being controlled by a central call processing server. In the event that a disturbance of a signaling path of the communications connection of the primary network is detected, an alternative connection for the signaling path is established via the secondary network, the signaling path of the primary network is logically linked to the created signaling path of the secondary network, and connection data, which were made available by means of the signaling path of the primary network, are made available for the signaling path of the secondary network.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Stage of International ApplicationNo. PCT/DE02/04397, filed Nov. 29, 2002 and claims the benefit thereof.The International Application claims the benefits of German applicationNo. 10158822.4 filed Nov. 30, 2001, both of the applications areincorporated by reference herein in their entirety.

FIELD OF INVENTION

This invention relates to a method for creating alternative connectionsto primary connections, particularly to voice-over IP connections(VoIP), in which the data transmission occurs in a primary network, andan alternative data transmission occurs in a secondary network which isoften less efficient. This method uses in particular a systemarchitecture with geographically distributed gateways, said gatewaysbeing controlled by a central call processing server (CPS).

BACKGROUND OF INVENTION

To aid understanding of the central idea on which the invention isbased, there follows below a brief explanation of the main aspects andcapabilities, advantages and disadvantages, of packet-switched datatransmission, which is used in the field of VoIP-applications, and alsoof the main embodiments of internet telephony according to the priorart.

In packet-switched networks, a type of transmission is implemented inwhich no continuous, physical channel is made available for aconnection. Instead, the message to be transmitted is divided at thetransmission end into small message packets—which are sometimes ofvarying lengths—which are provided with additional data for identifyingthe transmitter and receiver and are continuously numbered in theheader. These packets are then sent through the network individually,independently of one another. Each packet is analyzed in the individualnetwork nodes. Depending on the current network load, a decision is thenmade in the individual network nodes for each packet to determine viawhich outgoing connection the packet in question is to be forwarded tothe receiver. Consequently

the packets sometimes take different routes to the receiver depending onthe network utilization and are not received in the order in which theyare sent. For this reason the packets sometimes need to be buffered inthe individual network nodes and sorted in the receiver.

The advantages of packet-switching technology lie in good networkutilization and the facilitation of communication between terminals thathave different connection rates. However, packet-switched networks arerarely used for time-critical applications since a lot of time isrequired for the processing of the packets in the individual networknodes, the transmission paths of varying length, and the assembly anddisassembly of the packets.

The terms “internet telephony”, “IP telephony” and “voice-over IP”(VOIP) are used to describe a type of communication for transmittingvoice data between two communication parties via the internet and/or anintranet, in which computers or conventional fixed-network, cordless, ormobile telephones are used as communication terminals. In addition tovoice transmission and e-mail, fax and video services as well as voicemail are possible via the internet and/or intranet. The standardizationof hardware and software for these various forms of communication isoften referred to in the literature by the term “unified messaging”.

In internet telephony, two originally separate types of network areusually involved in the telephone network and the internet. Conventionaltelephone connections are normally used for the sections of the pathfrom the calling or called communication party to the nearest networkdial-in node. On the other hand, the internet is used for the sectionsof the path between the relevant network dial-in nodes, which areusually very much longer.

Various connection scenarios can result depending on which technology isused by the parties involved in an internet telephone call. Thecommunication flows either between different computers, between acomputer and a normal telephone, or between different telephones. Thisessentially means that there are four different variants of internettelephony:

Variant 1: Computer⇄Internet⇄Computer

In this variant, the user dials into the internet from his or hercomputer, e.g. a PC, via a “provider”. The user then tries to dial thefixed IP address of the required communication party via his or hertelephony software. If the computer of the required communication partyis connected to the internet and that party has loaded his or hertelephony software, he or she may receive the call. In this case thecomputers of the two communication parties are connected via the PSTN(public switched telephone network) to an ITSP (internet telephonyservice provider), from where they can transmit voice data in thepacket-switched internet.

Variant 2: Computer⇄Internet⇄Telephone

In this variant the user dials into the internet from his or hercomputer via his or her provider. He or she then dials the number of therequired communication party using the telephony software. The datapackets are sent by the software to a gateway that is nearestgeographically to the required communication party. Gateways are specialinterfaces between networks of different network operators or nationalnetworks, which link together private branch exchanges or switchingcenters via the internet and are used for recording call charges,converting different signaling procedures, and for speed adaptation.With the help of gateways, it is possible—for example—to telephone fromone conventional telephone connection to another conventional telephoneconnection by dialing the telephone number and using a special internetaccess code. The voice data is transferred to the local PSTN from thenearest gateway. This method places great demands on the supplier'sinfrastructure. To enable internet telephony to be providedcost-effectively, at least one gateway between the internet and thelocal telephone network must be installed in every country in the world.

Variant 3: Telephone⇄Internet⇄Computer

To reach a telephone via a computer, it is necessary to set up aconnection to an internet telephone service provider. Only then can therequired communication party be dialed. For this procedure to work, itis necessary for the computer of the required communication party to beswitched on, for their telephony software to be loaded and for theircomputer to be connected to the internet.

Variant 4: Telephone⇄Internet⇄Telephone

In this solution the user dials into a gateway from his or her telephoneconnection via the circuit-switched PSTN. After dialing into a gatewaythe user dials the internet access code or PIN “Personal IdentificationNumber” allocated to him or her by the network operator, and finally thedestination call number of the required communication party. From thedialed destination call number or part thereof, the gateway system thendetermines which gateway is geographically nearest to this destinationusing a routing table. The gateway—for its part —is identifiable by anIP address, and requires this in order to implement a connection to therequired communication party via their local PSTN. As soon as thishappens, the calling communication party receives a signal and can

speak. The voice data is transmitted via the internet usingpacket-switching technology.

All four variants can be implemented either via the worldwide internetor via a corporate or organizational intranet, with intranets havingbetter transmission quality as a rule.

A fundamental element of an internet telephony system is the callprocessing server (CPS), often also known as the gatekeeper. Thisconsists of a series of software applications that run on one or moreservers. These may be located at any point within the logical IPnetwork. In its simplest form, a CPS provides an overview of the statusof all clients belonging to a certain domain. Its functions are definedaccording to the H.323 standard of the International TelecommunicationsUnion (ITU). These functions include the resolution of addresses (fromE.164 to IP and vice versa) and various authentication and authorizationtasks, central call processing, and routing. In addition, it conductsswitching functions (call control including call setup and call release)for clients and gateways within the IP network and manages a database inwhich user profile and network configuration information is stored. Thefunctionality provided by the CPS does, however, vary greatly from onemanufacturer to another.

If individual voice channels cannot be switched via the internet andalternative connections to the voice-over IP connection must be switchedvia circuit-switched networks, the great variety of features of the VOIPconnection that can be controlled by the CPS are sometimes lost to theuser. In this case, certain features—such as, for example, the settingup of conference calls—can no longer be used.

An essential characteristic of circuit-switched and/or packet-switcheddata traffic in the ISDN is the consistent separation between thetransmission of signaling data and useful data, which is carried out ondifferent channels. Of primary importance in this are the so-called Band D channels. A first B-channel with a data transfer rate of 64 kbpsis used for the transfer of digitized voice signals. In parallel to thisthe user may be offered a second B-channel for transmitting data, whichlikewise has a data transfer rate of 64 kbps. At the same time acomplete So interface is provided which permits up to eight differentcommunication terminals to be connected for each user, even if a dataconnection is not expected to be present at the telephone of a user.This means that both B-channels are always available in bothcommunication directions and that several communication terminals can beactive at the same time, each of them using one of the two B-channelssimultaneously. In contrast, a D-channel with a data transfer rate of 16kbps (D₁₆) or 64 kbps (D64) is used in addition for the transfer ofsignaling data. Besides the exchange of signaling data, users can alsosend data packets to the network on the D-channel, and these areforwarded in turn by the network to other communication parties.However, unlike in the case of the B-channel, connections cannot be setup via the D-channel.

According to the prior art, the strict separation of signaling anduseful data guarantees that the user does not have to suffer any loss ofinformation or features, even if the useful data is diverted via analternative network, since the D-channel always transfers the signalingand control information correctly.

SUMMARY OF INVENTION

Starting from the above prior art, this invention dedicates itself tothe task of providing a method which can be used to set up alternativeconnections to primary connections, in which the data transfer takesplace via a primary network or, alternatively, via a

secondary network, whereby the established features are retained as faras possible when data is switched to alternative connections.

This object is resolved according to the invention by the features inthe independent claims. Advantageous exemplary embodiments, whichfurther develop the ideas behind the invention, are defined in thedependent claims.

The invention relates to a method for making available alternativeconnections to primary connections, in particular to voice-over IPconnections, with the help of a call processing server. A systemarchitecture with geographically distributed gateways can be used inthis context, said gateways being controlled via the central callprocessing server. At the same time the standardized call-processingoperations for accessing a circuit-switched network can be assumed inthe context of a converging network solution without modification.

BRIEF DESCRIPTION OF THE DRAWINGS

Other properties, features, advantages and applications of the inventionensue from the dependent claims and from the following description of anexemplary embodiment of the invention, which is illustrated by thefollowing drawings.

In these,

FIG. 1: is a simplified block diagram 100 illustrating an exemplaryalternative connection to a packet-switched VOIP connection, and

FIGS. 2 a, b: is a flowchart 200 illustrating the provision ofalternative connections to packet-switched VOIP connections viacircuit-switched networks.

DETAILED DESCRIPTION OF INVENTION

The functions of the components contained in an exemplary embodiment ofthe invention, as illustrated in FIGS. 1 and 2, are described in greaterdetail below.

Firstly, the invention is to be explained schematically with referenceto FIG. 1. A simplified block diagram is shown to illustrate the systemarchitecture used in the solution according to the invention, withgeographically distributed IP shelves or gateways 102 a, 102 b and acall processing server 104. In this context, an example of apacket-switched voice-over IP connection is shown between twocommunication parties A and B connected via terminals 101 a, 101 b andgateways 102 a, 102 b, whereby—in the illustrated scenario—both asignaling path 107 a (D-channel) and a useful data path 107 b(B-channel) of the voice-over IP connection are interrupted.Communication party A is allocated the terminal identification code#A:2000, and communication party [B] is allocated the terminalidentification code #B:3000. Since the signaling path 107 a and theuseful data path 107 b can no longer be switched via the internet 106 b,alternative routes to the voice-over IP connection are switched viaalternative networks. In the exemplary embodiment shown in FIG. 1, analternative network 106 c is used for the signaling path 107 a and acircuit-switched network 106 a is used as an alternative network for theuseful data path 107 b. In the latter case, for example, the publicswitched telephone network (PSTN) of Deutsche Telekom might be used.

For the two communication parties A and B involved in the voice-over IPconnection via the terminals 101 a, 101 b and the gateways 102 a,

102 b, the failure of the voice-over IP connection via the internet 106b is not noticeable since the alternative connection provides the samerange of functions as the voice-over IP connection, as explained below.

FIG. 2 shows a flow chart illustrating the method according to theinvention for providing alternative connections to packet-switchedvoice-over IP connections via circuit-switched networks, in four stages.The individual stages of the method are explained in detail below.

Stage #1:

Firstly, in a substage 202, the terminal identification code #B:3000 ofthe communication terminal 101 b of subscriber B to be called is dialedfrom the communication terminal 101 a of subscriber A with the terminalidentification code #A:2000, and the connection request is signaled tothe call processing server 104. In the next substage 204, the callprocessing server 104 detects that the useful data path 107 b is notavailable through the primary network 106 b (in this case thepacket-switched internet) e.g. because a faulty router has been switchedoff, as a result of poor transmission quality, etc.

Stage #2:

Since the signaling path 107 a from the call processing server 104 tothe gateways or access points 102 a, 102 b of the communicationterminals 101 a, 101 b must always be available, this means that thesignaling path 107 a is either still available through the primarynetwork 106 b, or—as is to be assumed in this example—has been switchedto an alternative network 106 c. It is therefore necessary to ascertain,in a further substage 206, which of the two options applies.

Stage #3:

If the signaling path 107 a has been rerouted to the alternative network106 c, the call processing server 104 signals to the gateway 102 a, in asubstage 208, that it must dial an alternative call number #B:0-1234567in order to reach the communication terminal 101 b of subscriber B. Inthe exemplary embodiment outlined in FIG. 1, the alternative call numberis #B:0-1234567. The preliminary “0” here represents the access code toa circuit-switched network 106 a. (Switching to other circuit-switchednetworks is a standard procedure already implemented in many cases formaintaining telephone connections conducted via circuit-switchedtelephone networks.) In a further substage 210, the call processingserver 104 then stores the features of this communication connection andthe link between the originally dialed call number #B:3000 and thealternative call number #B:0-1234567.

Stage#4:

A connection request arriving at gateway 102 b by means of thealternative call number #B:0-1234567 is signaled to the call processingserver 104 in a substage 212. In the next substage 214, the callprocessing server detects that it is the incoming part of an alternativeconnection, whereupon, in a further substage 216, the said callprocessing server 104 calls up the features of the correspondingcommunication connection stored in stage 210 and—in a final substage218—signals the incoming connection request to communication terminal101 b of subscriber B, just as if the useful data and signaling data ofthe VoIP connection had never been routed via alternative networks 106a+c.

Therefore, in the context of the invention, the outgoing connectionrequest from communication terminal 101 a of communication party A to acircuit-switched network 106 a, and the incoming connection request fromthe circuit-switched network 106 a to communication terminal 101 b ofcommunication party B (i.e. the outgoing and incoming part of analternative connection via the circuit-switched network), are identifiedas being related, as explained above. A link is then established betweenthe outgoing part and the incoming part of the alternative connection.This takes place in the central call processing server 104, since thisis where the data for an internal connection is stored anyway. Allfeatures are then permitted for this connection—provided, of course,that the signaling paths 107 a to the gateways 102 a, 102 b remainfunctional.

The link between the outgoing part and the incoming part of thealternative connection can be generated in various ways depending on thetype of alternative network and alternative connection, for example viathe dialed call number, where the alternative connection uses an analogtrunk circuit.

Another option is the use of the dialed call number and an artificialcalling party number, if digital trunk circuits with a plurality ofB-channels are used. In this case the user access is via a primary rateinterface (PRI).

In the method according to the invention, an incoming alternativeconnection is signaled first via the (alternative) signaling path 107 ato the call processing server 104. The said call processing server, onthe basis of the link, detects that the communication connection is anincoming alternative connection and links it to the outgoing part of thealternative connection. The call processing server 104 then calls up theconnection data and features of the communication connection (e.g. callwaiting, call diversion, conference call, etc.) and sends them via the(alternative) signaling path 107 a. Thus the connection appears to thecalled connection terminal 101 b to be an internal connection, eventhough an alternative route has been used.

In an exemplary embodiment of the invention, provision is made inaddition for the type of link between the outgoing and incoming part ofthe alternative connection, such that a separate alternative number isnot required for each communication terminal 101 b called. Instead, analternative call number can be dynamically allocated from a quantity ofalternative call numbers with the help of the call processing server104. The advantage of this method is that less use is made of exchangenumbers, thus enabling considerable cost savings to be achieved.

This invention can generally be used to make alternative connections viathe public telephone network appear to the user as internal connections,with all internal features remaining available, even when alternativeconnections are used.

In particular, this invention can be used advantageously in anarchitecture in which the individual geographically distributed gateways102 a, 102 b are connected with communication terminals of a privatebranch exchange within the IP network 106 b.

1.-14. (cancelled)
 15. A method for creating an alternative connectionto a communication connection from a first subscriber via a primarynetwork to a second subscriber, the communication connection having auseful data path and a signaling path, the method comprising: detectinga fault in the signaling path of the communication connection of theprimary network; creating an alternative connection for the signalingpath via an alternative network, independently of the useful data path;logically linking the signaling path of the primary network with thecreated signaling path of the alternative network; and storing offeatures of the communication connection of the primary network relatingto connection data which is provided by the signaling path of theprimary network, so that they are also made available for the signalingpath of the alternative network.
 16. A method according to claim 15,wherein the outgoing part of the alternative connection is linked withthe incoming part by means of the link from the signaling path of theprimary network to the signaling path of the alternative network, andwherein the stored connection data is called and transferred via thesignaling path of the alternative network.
 17. A method according toclaim 15, wherein a packet-switched network is used as the primarynetwork and a circuit-switched network is used as the alternativenetwork.
 18. A method according to claim 16, wherein a packet-switchednetwork is used as the primary network and a circuit-switched network isused as the alternative network.
 19. A method according to claim 17,wherein the internet and/or a corporate or organizational intranet isused as the packet-switched primary network.
 20. A method according toclaim 17, wherein a public telephone network is used as acircuit-switching alternative network.
 21. A method according to claim19, wherein a public telephone network is used as a circuit-switchingalternative network.
 22. A method according to claim 15, wherein atransfer of digitized voice signals via a voice-over IP connection isused as the communication connection.
 23. A method according to claim15, wherein a transfer of digitized data signals via a an internet orintranet connection is used as the communication connection.
 24. Amethod according to claim 15, wherein a multimedia transfer of digitizedvideo and/or audio signals via an internet or intranet connection isused as the communication connection.
 25. A method according to claim15, wherein in the case of an invalid useful data path, between acalling terminal allocated to the first subscriber and a called terminalallocated to the second subscriber, the following steps are performed:requesting a gateway of the calling terminal to reach the calledterminal under an alternative call number for the alternative network;storing the features of the invalid useful data path; linking theoriginally dialed call number and the alternative call number; recordingthe incoming connection request at the gateway of the called terminal;identifying the incoming part of the alternative communicationconnection; requesting the stored features of the interruptedcommunication connection; and signaling the incoming connection requestto the called terminal.
 26. A method according to claim 25, wherein thelink between the outgoing part and the incoming part of the alternativeconnection is created via a dialed call number, if this call number usesan analog trunk circuit.
 27. A method according to claim 25, wherein thelink between the outgoing part and the incoming part of the alternativeconnection is created via a dialed call number and an artificial callingparty number, if digital trunk circuits with a plurality of B-channelsare used.
 28. A method according to claim 25, wherein in the linkbetween the outgoing and incoming part of an alternative connection analternative call number for the called terminal is dynamically allocatedfrom a quantity of reusable alternative call numbers with the help ofthe call processing server.
 29. A method according to claim 26, whereinin the link between the outgoing and incoming part of an alternativeconnection an alternative call number for the called terminal isdynamically allocated from a quantity of reusable alternative callnumbers with the help of the call processing server.
 30. A callprocessing server for executing switching functions on the internet,wherein the server is adapted for performing a method for creating analternative connection to a communication connection from a firstsubscriber via a primary network to a second subscriber, thecommunication connection having a useful data path and a signaling path,the method comprising: detecting a fault in the signaling path of thecommunication connection of the primary network; creating an alternativeconnection for the signaling path via an alternative network,independently of the useful data path; logically linking the signalingpath of the primary network with the created signaling path of thealternative network; and storing of features of the communicationconnection of the primary network relating to connection data which isprovided by the signaling path of the primary network, so that they arealso made available for the signaling path of the alternative network.31. A software application for operating a call processing serverlocalized on the internet, the application implementing a method forcreating an alternative connection to a communication connection from afirst subscriber via a primary network to a second subscriber, thecommunication connection having a useful data path and a signaling path,the method comprising: detecting a fault in the signaling path of thecommunication connection of the primary network; creating an alternativeconnection for the signaling path via an alternative network,independently of the useful data path; logically linking the signalingpath of the primary network with the created signaling path of thealternative network; and storing of features of the communicationconnection of the primary network relating to connection data which isprovided by the signaling path of the primary network, so that they arealso made available for the signaling path of the alternative network.